Variable speed hydraulic motors



May 12, 1970 G. IFE ETAL 3,511,135

VARIABLE SPEED HYDRAULIC MOTORS Filed Oct. 22 1968 4 Sheets-Sheet 1 May 12, 1970 ca. lFE ETAL 3,

VARIABLE SPEED HYDRAULIC MOTORS Filed Oct. 22 1968 4 Sheets-Sheet 2 :May 12, 1970 G. IFE ETAL 3,511,135

VARIABLE SPEED HYDRAULIC MOTORS Filed Oct. 22 1968 4 Sheets-Sheet t5 May 12, 1970 5 [FE EIAL 3,511,135

VARIABLE SPEED HYDRAULIC MOTORS Filed Oct. 22 1968 4 Sheets-Sheet l SPEED CONTROL S'GNAL CONTROL 94 PRESSURE SUPPLY SOURCE MOTOR INPUT PRESSURE SlGNAL lNPUT PRESSURE SENSlTlVE DEVICE United States Patent U.S. Cl. 91483 6 Claims ABSTRACT OF THE DISCLOSURE This invention is concerned with a variable-speed hydraulic motor having axial and radial pistons arranged in pairs with intercommunicating cylinders. In the preferred arrangement the axial pistons co-operate with a stationary swashplate of fixed inclination, while the radial pistons co-operate with a surrounding circular eccentric cam of which the eccentricity can be varied to vary the motor speed.

This invention is concerned with variable-speed hydraulic motors having pistons of which the displacement is adjustable to vary the motor speed.

A motor according to this invention has a rotary cylinder barrel which is connected to an output shaft and which contains substantially axially extending pistons which drive the barrel by engagement with a stationary inclined swashplate, the axial pistons being housed in cylinders in the barrel each of which communicates with a radial cylinder containing a radially movable piston co-operating with a surrounding eccentric cam which causes the radial pistons to move in and out during each revolution of the cylinder barrel. The displacement of the motor (and consequently the speed) is preferably varied by varying the degree of eccentricity of the cam; alternatively it could be varied by varying the inclination of the swashplate.

The cam is preferably circular and may, for example, contain a stationary outer race which surrounds a rotary inner race engaged by the radial pistons, with balls or rollers interposed at circumferential intervals between the inner and outer races.

A motor according to this invention can be designed for optimum efliciency operation at its highest speed with the cam set at zero eccentricity, so that the cylinder barrel is driven purely by the axial pistons. Increasing the eccentricity of the cam in the appropriate direction then increases the displacement of each pair of axial and radial pistons and therefore decreases the motor speed. A motor according to this invention can be readily designed to operate at a constant flow and at a constant pressure, and can be arranged to be powered by a relatively simple and inexpensive fixed-capacity pump such as a gear pump (assuming that the pump is driven at a fixed speed).

An example of a motor according to this invention is shown in the accompanying drawings. In these drawings:

FIG. 1 is an axial section of the motor taken on the line II in FIG. 2;

FIG. 2 is a transverse section of the motor taken on the line II-II in FIG. 1;

FIG. 3 is a transverse section of a modified form of the motor shown in FIGS. 1 and 2; and

FIG. 4 shows diagrammatically a control arrangement for the motor or the modified form of motor.

The motor includes a cylinder barrel 2 which is connected to an output shaft 4 via a circular plate 6 which is welded to the shaft and is secured to the cylinder barrel by bolts 8. The cylinder barrel is housed within a casing defined by end parts 10 and 12 secured to approximately octagonal plates 14 and 16 respectively by bolts (not shown) passing through flanges 18 and 20, the plates 14 and 16 being secured by bolts 22 to opposite sides of a further octagonal plate 24.

Five circumferentially spaced axial pistons 26 are slidably housed in cylinders 28 in the cylinder barrel and each terminates at its outer end in a part-spherical part engaging a slipper 30 which in turn bears on a fixed inclined swashplate 32; the slippers are held against the swashplate by a ring 34. It will be appreciated that the pistons 26 co-operate with the swashplate 32 to drive the cylinder barrel 2 in the manner of a conventional swashplate motor.

The shaft 4 is carried by a ball bearing 36 in the housing end part 10, while the cylinder barrel itself is mounted within roller bearings 38 and 40 within the octagonal plates 14 and 16. The bearing 38 may, however, be omitted.

Hydraulic fluid is delivered to and from the cylinders 28 via a stationary valve plate 42 which bears against the cylinder barrel, being held firmly in contact with the cylinder barrel by fluid pressure. The valve plate communicates with external inlet and outlet ports 44 via short metal sleeves 46 each of which engages with one end in the valve plate and with its other end in the end part 12 of the motor casing. Each sleeve 46 is a tight fit in the casing part 12 but is a clearance fit in the valve plate so that the valve plate can move universally to a slight degree with respect to the sleeves 46; this enables the valve plate to remain in firm contact with the cylinder barrel. O-rings 48 maintain a seal between the sleeves 46 and the valve plate.

The valve plate 42 delivers hydraulic fluid to and from the cylinders 28 through two kidney-shaped ports 50 and 52 which are mirror images of one another on opposite sides of a central plate passing through the pump axis. The ports 50 and 52 communicate with the cylinders 28 through narrow passageways 54, of which there is one for each cylinder.

There may be two inlet sleeves 46 in parallel and two outlet sleeves.

In circumferential alignment with each cylinder 28 there is a radial cylinder containing a radial piston 56. Each piston 56 is pivoted to a slipper 60 by means of a part-cylindrical projection 58 on the slipper (see FIG. 2) which seats in a corresponding part-cylindrical recess in the end of the piston. Each slipper has flanges 62 on opposite sides (see FIG. 1) by which it is trapped in a composite ring formed by ring parts 64 and 66 which are secured together by screws (not shown). The flanges also project laterally as viewed in FIG. 2. The ring parts 64 and 66 lie immediately within an inner race 68 which is surrounded by an outer race 70 with interposed trapped rollers 72. The outer race 70 remains stationary while the inner race 68 rotates with the cylinder barrel 2. Slight circumferential sliding of each slipper with respect to the inner race 68 must occur during use, and to assist this movement the convex outer surfaces of each slipper may have a coating, for example of silver, to reduce the coeflicient of friction.

The outer race 70 is housed within a cam member 74 which has a circular interior and an octagonal exterior as shown in FIG. 2. Two opposite facets 76 of the octagonal exterior serve as guide faces co-operating with corresponding facets of the inner surface of the plate 24. The facets 76 ensure that the cam member 74 can move only in the direction of the section line II shown in FIG. 2.

In use, in order to obtain the maximum speed, the cam member 74 is set by means of locating screw-threaded spindles 78 at zero eccentricity, that is to say with the inner surface of the cam member coaxial with the cylinder barrel, so that no reciprocation of the radial pistons takes place, the motor displacement then being provided purely by the axial pistons 26. In order to reduce the motor speed, the cam member 74 is moved in an upward direction so that the action of the cam on the radial pistons is to move each radial piston radially outwards as its corresponding axial piston moves axially out of the cylinder barrel. The speed reduces as the degree of eccentricity of the cam member 74 increases. A motor according to this invention can readily be arranged tohave a speed rato (i.e. a ratio of maximum to minimum speed) of up to :1 this facilitates use in various applications, for example various machine carriage or tool drives, and coiler drives, for which the drum speed may need to change considerably as winding progresses in order to keep substantially constant the speed or tension of the material being wound.

It will be appreciated that the degree of eccentricity of the cam member 74 is varied by screwing in one of the spindles 78 and screwing out the other. As an alternative, the cam member position may be controlled by means of oppositely disposed pistons 80, of which there are two on each side on opposite sides of the spindles 78, by supplying controlled high-pressure hydraulic fiuid to the pistons through unions 82; in this way the motor speed can be made subject to remote control, the spindles 78 being screwed out so as to be inoperative.

Lubricating oil for the cylinder barrel bearings is injected through a port 84.

Various modifications of the motor are possible. For example, as shown in the FIG. 3 the outer bearing faces of the slippers 60 may be arranged as hydrostatic bearings, for example with oil directed to the bearing interface through bores 86 extending through the pistons 56 and slippers 60; in other words the oil supply for the hydrostatic bearing surfaces is obtained from the cylinders containing the pistons 56. In this case the roller bearing constituted by the races 68 and 70 and rollers 72 are omitted, and the slippers bear directly on the inner cylindrical surface of a lining sleeve 88 in the cam member 74.

The cam eccentricity may be controlled purely hydraulically, for example as shown in 'FIG. 4 by means of two pistons 90 (like the pistons 80 but larger) lying diametrically on opposite sides of the cam 74. In this case the hydraulic circuit 92 controlling the cam pistons 90 may include means 94 for overriding the control signal (supplied at 96) in the event of the motor failing to start in a high-speed setting (that is to say, with the cam. 74 set at zero eccentricity or nearly so), so as to move the cam and thus provide an increased starting torque. For example, the means 94 for controlling the pressure of fluid supplied to the cam pistons 90 may be subject to control by means of a device 98 sensitive to the pressure of the driving fluid at the motor input 44; in the absence of the pressure drop which occurs when the driving fluid is flowing through the motor, the fluid pressure would be at the full supply value, and the arrangement is such that the presence of the full supply pressure in say a servo-valve constituting the means 94 overrides the control signal (supplied at 96) to the cam pistons and moves the cam upwards as viewed in the drawings.

We claim:

1. A variable-speed hydraulic motor comprising an output shaft; a rotary cylinder barrel connected to the output shaft; means defining a plurality of circumferentially spaced axial cylinders in the cylinder barrel; a plurality of axial pistons which are slidable in the axial cylinders and project out of one end of the cylinder barrel; an inclined s'washplate engageable with the axial pistons to cause each axial piston to move into and out of the cylinder barrel during each revolution of the cylinder barrel; means defining a plurality of radial cylinders in the cylinder barrel, each communicating with one of the axial cylinders and each containing a radial piston which projects radially out of the cylinder barrel; an eccentric cam which surrounds the cylinder barrel and causes each radial piston to move in and out in phase with the associated axial piston; means for delivering hydraulic fluid to and from the cylinders; and means for varying the stroke performed during each revolution by at least one of the two sets of pistons.

2. A motor according to claim 1 in which the stroke of the radial pistons is variable by varying the degree of eccentricity of the earn.

3. A motor according to claim 2 in which the degree of eccentricity of the cam is controlled by hydraulic control pistons bearing on opposite sides of the earn, the cam being laterally movable under the control of the hydraulic control pistons.

4. A motor according to any of claims 1 to 3 in which hydraulic fluid for powering the motor is fed to and from the cylinders through a stationary valve plate at one end of the cylinder barrel.

5. A motor according to claim 2 or claim 3 in which the cam surrounding the cylinder barrel is circular and contains a stationary outer race which surrounds a rotary inner race engaged by the radial pistons, with balls or rollers interposed at circumferential intervals between the inner and outer races.

6. A motor according to claim 1 in which the radial pistons have slippers at their outer ends through which they slidably engage the cam, the outer bearing surfaces of the slippers being formed as hydrostatic bearings.

References Cited UNITED STATES PATENTS 1,987,781 1/1935 Maw 91-205 2,678,536 5/1954 Morgan 91-175 2,989,005 6/1961 Gardineer 91-205 3,081,708 3/1963 Nyman et al. 91-205 PAUL E. MASLOUSKY, Primary Examiner US. Cl. X.R. 

